How to test a surge supressor

Discussion in 'General Electronics Chat' started by jfv, Aug 16, 2012.

  1. jfv

    Thread Starter New Member

    Aug 14, 2012
    Hi everyone,

    I was wondering how can I test a surge suppressor to see if it is still working properly? It's a TrippLite Isobar rack mount type with no indicators on it to let me know if the MOVs has been compromised?


  2. #12


    Nov 30, 2010
    I tried this once and failed. Then I phoned the manufacturer and the only thing they had to say was, "You can't test them".

    However, the theory is that a high voltage pulse will be attenuated. If you can set up a thousand volt pulse and watch the results on an oscilloscope, you should have a result.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Well... what is the suppressor rated to handle? Give me a rating and I may be able to suggest a test.

    Here's a story: Back when I was doing power supplies one product needed a qualification test to see if it would safely isolate itself from the AC line for a fault. Isolation was achieved by using a huge (size of a frozen orange juice can) SCR to short the input and literally fuse the input wiring. Hey, the method was in the unit design spec for this military supply.

    So... unit was wired up, fault simulated and... the breaker in the power panel opened. So the unit was moved to the AC panel to the main breaker, the fault simulated and... our entire company went dark till the main breaker was reset.

    So.. after some discussion the unit was connected before the main breaker to the power coming into the building. The fault was simulated and... the whole town went dark for 3 hours.

    They didn't ask us and no one told.

    The unit was then redesigned with smaller wire. I am happy to say I was not involved with this effort, but I did get the afternoon off.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I believe the proper way to test a MOV (removed from the system) by measuring/comparing leakage current to the manufacturers rating.

    I've heard of others doing it by isolating it and simply measuring its resistance.

    Obviously visually looking to see if its burnt/destroyed then replacing it is usually the best/easiest method.
  5. DMahalko

    AAC Fanatic!

    Oct 5, 2008
  6. #12


    Nov 30, 2010

    I found the answer for you. He wants to know if the MOVs have been compromised.
  7. westom


    Nov 25, 2009
    An answer is found in MOV datasheets. The test is also not very useful for your purpose. Especially when properly sized protectors remain functional even after direct lightning strikes and do protection even decades later.

    Let's start with the light. It reports a type of failure that must not happen. A catastrophic failure that MOV manufacturers say is completely unacceptable. In some cases, may be a human safety threat. MOVs must fail only by degrading. That light can never report the acceptable type of failure.

    That light reports when a protector was overwhelmed by a surge. Same surge also struck adjacent appliances simultaneously. Why were other household appliances also not damaged? Undersize a protector to fail on a surge that is not typically destructive. The surge can damage a protector but not any appliances. Then naive consumers (who also do not read manufacturer spec numbers) will recommend that protector.

    That light only reports when the protector was grossly undersized. Read MOV datasheets to understand this and to also learn how to test for a degraded protector.